This invention relates to an analog reproducer unit for the exploration vessel which retrieves seismic records produced in an ocean-bottom seismometer.
T. J. G. Francis et al, "Marine Geophysical Researches" (1975), 195-213, describe three ways of retrieving seismic information from the ocean floor. A self-contained instrument may be attached by a rope to a surface ship or buoy; a transducer package may telemeter its data to a surface ship buoy or land station for recording; and a completely independent instrument of the "pop up" type may record data in its self-contained memory. The latter type instrument has been referred to as an on-bottom seismometer. These instruments have the advantage that they are easier to place on a particular bottom feature; the instrument is more secure from being tampered with than one which is connected to a surface buoy, and less system generated noise is associated with this type of instrument than one employing a mooring or a telemetry link.
Attempts to use ocean-bottom seismometers for refraction surveys have generally used a continuously running tape recorder to record the data. Avedik et al, "Ocean Bottom Refraction Seismograph (OBRS)", Marine Geophysical Researches 3 (1978), 357-379, describes an ocean bottom seismometer used for refraction surveys. In this system the seismic data are encoded with pulse width modulation. A tape recorder is set to start at a preset time. This tape recorder runs continuously at a very low speed to record the pulse width modulated data. U.S. Pat. No. 4,138,658--Avedik et al discloses and claims some features of this unit.
Johnson et al, "A Direct Recording Ocean Bottom Seismometer", Marine Geophysical Researches 3 (1977), 65-85, describes another system using a continuously running tape recorder.